Adhesion promoting polymeric materials and planographic printing elements containing them

ABSTRACT

A planographic printing element suitable to receive and bond with a subsequently applied hydrophilic layer comprises a substrate layer such as polyester film or paper having coated thereon an adhesion layer, said adhesion layer comprising a polymer having a glass transition temperature of less than 15° C. and containing functional groups such as hydroxyl, epoxy or glycidyl capable of reacting with the hydrophilic layer. The polymer may be a terpolymer of a hydroxyalkylacrylate, an alkyl acrylate and an aminoalkylmethacrylate. The polymer may be mixed with gelatin and the mixture applied to the substrate as a coating.  
     The hydrophilic layer comprising a mixture of alumina and titania particles in a sodium silicate binder is subsequently applied as a coating to the adhesion layer.

FIELD OF THE INVENTION

[0001] This invention relates to planographic printing elements and amethod for their preparation.

BACKGROUND OF THE INVENTION

[0002] One form of planographic printing is lithographic printing whichrelies on the immiscibility of oil and water, wherein the oily materialor ink is preferentially retained by the image area of a lithographicprinting plate. When a suitably prepared surface is moistened with waterand an ink is then applied, the background or non-image area retains thewater and repels the ink while the image area accepts the ink and repelsthe water.

[0003] The ink on the image area is then transferred to a surface of amaterial upon which the image is to be reproduced, such as paper, clothand the like. Commonly the ink is transferred to an intermediatematerial called the blanket which in turn transfers the ink to thesurface of the material upon which the image is to be reproduced.

[0004] The production of printing elements for use in lithographicprinting requires the formation of a hydrophilic layer on a substrate.

PROBLEM TO BE SOLVED BY THE INVENTION

[0005] There is a continuing need to improve the adhesion between thehydrophilic layer and the substrate on which it is based. The presentinvention provides a solution to this problem by providing aplanographic printing element in which the hydrophilic layer is bound tothe substrate by a selected polymer.

SUMMARY OF THE INVENTION

[0006] According to the present invention there is provided aplanographic printing element suitable to receive and bond with asubsequently applied hydrophilic layer said element comprising:

[0007] (i) a substrate layer having coated thereon

[0008] (ii) an adhesion layer, said adhesion layer comprising a polymerhaving a glass transition temperature of less than 15° C. and containingfunctional groups capable of bonding with a hydrophilic layer when thelatter is applied as a coating.

ADVANTAGEOUS EFFECT OF THE INVENTION

[0009] By the use of the polymeric layer containing functional groupscapable of bonding with groups in the hydrophilic layer, the adhesion ofthe hydrophilic layer to the substrate is significantly increased and animproved printing element provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a schematic drawing showing a planographic printingelement according to the invention.

[0011] FIGS. 2 to 5 are graphs which show how the adhesion rating varieswith polymer laydown for polymers A,B,C and D.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The term polymer in the present specification is intended toinclude copolymers and terpolymers unless the context requiresotherwise.

[0013] The Adhesion Layer

[0014] Examples of suitable functional groups contained in the polymerare hydroxyl, epoxy, glycidyl and groups such as halide or sulphonateester which are capable of being displaced by a nucleophilic group.

[0015] Typical functional groups in the hydrophilic layer are —Si—OH,hydroxyl or alkoxide.

[0016] The polymer is conveniently obtained by the polymerisation of amonomer containing the functional groups.

[0017] The polymers applied as the adhesion layer may comprise latexpolymers prepared from monomers containing functional groups that canreact with corresponding groups in the hydrophilic layer by eithercondensation or addition reactions.

[0018] Examples of such functional groups include hydroxyl and epoxy, anexample of epoxy being a glycidyl group.

[0019] The polymer may contain from about 25 to 85 weight %, preferablyabout 35 to 55 weight % of monomers containing such units.

[0020] Suitable polymers are those of hydroxyalkylmethacrylates such as2-hydroxyethylmethacrylate.

[0021] A co-monomer may be employed to assist in obtaining requiredglass transition temperature of less than 15° C. An example of such aco-monomer is an alkyl acrylate such as butyl acrylate. The co-monomermay be present in amount from 15 to 75 weight %, preferably 45 to 65weight %.

[0022] A further co-monomer may be added to cross-link with gelatin byuse of conventional gelatin hardeners (e.g. bis(vinylsulphonyl)methaneor the like,) in 0.5-10 weight %, preferably 1 to 7 weight %.

[0023] An example of such a co-monomer is an aminoalkyl acrylate such as2-aminoethyl methacrylate hydrochloride.

[0024] The % by weight are based on the combined weight of the monomerspresent.

[0025] A class of preferred polymers are terpolymers of (a) ahydroxyalkylacrylate, (b) an alkyl acrylate and (c) anaminoalkylmethacrylate.

[0026] Typical relative amounts of the monomers are: (a) from about 20to about 80 (b) about 20 to about 70 and (c) from about 2 to about 10.

[0027] Another preferred class of polymers are copolymers of (i)glycidyl methacrylate and (ii) an alkyl acrylate.

[0028] Typical relative amounts of monomer (i) are from 90 to about 50of monomer, and monomer (ii) from about 10 to about 50.

[0029] The polymers may be prepared by latex or solution polymerisation.Suitable preparations are described in U.S. Pat. No. 4,689,359.

[0030] This patent discloses that the adhesion of a coating compositioncontaining gelatin to a discharge treated polyester film support can beimproved by incorporating in the gelatin one or more defined polymers.The problem with which this patent is concerned is the bonding of agelatin-containing composition to a polyester support used for makingphotographic elements. In contrast, the problem addressed by the presentinvention is the bonding of the support (which may be polyester) to ahydrophilic layer employed in the preparation of planographic printingelements.

[0031] The polymers employed in the present invention may be blendedwith gelatin and the composition thereby obtained applied as a coatingto the substrate.

[0032] The polymer/gelatin compositions may have a ratio of polymer togelatin in the range 95:5 to 5:95 by weight, and more desirably between95:5 and 40:60.

[0033] The laydown of polymer or polymer gelatin composition on thesubstrate is conveniently at least 50 mg/square metre to 4 g/squaremetre, preferably from 100 mg/square metre to 500 mg/square metre.

[0034] When the polymer is applied with gelatin it is preferred thatgelatin provides not more than about 60% by weight of the composition ofpolymer and gelatin.

[0035] Typical thicknesses of the polymer coating are from about 0.05microns up to about 4 microns.

[0036] Such polymer and polymer/gelatin compositions may also includesurfactants to provide suitable wetting characteristics, opaque orcoloured materials to provide suitable backgrounds, conducting materialsto provide anti-static qualities and cross-linking agents to providesufficient robustness. In addition, materials to adjust pH, particularlyto achieve specific conditions intended to facilitate a reaction with anoverlying layer, can also be included. These compositions can be coatedas a single layer or as a part of multilayer structure.

[0037] Suitable polymers and their method of preparation are describedin U.S. Pat. Nos. 4,695,532 and 4,689,359.

[0038] The Substrate

[0039] The substrate may be any one of those known in the planographicprinting art. For example the substrate may comprise a polyester filmsuch as polyethylene terephthalate, cellulose acetate film, or otherpolymer film such as polyethylene or paper such as resin coated paper.

[0040] The Hydrophilic Layer

[0041] The hydrophilic layer may comprise inorganic oxide particles suchas a metal oxide particles, for example aluminium oxide and titaniumdioxide together with a binder such as sodium silicate. Suitablehydrophilic layers and their preparation are described in WO 97/19819and European Patent Application No 963859A the disclosures of which areincorporated by reference.

[0042] According to another aspect of the invention a planographicprinting element comprises:

[0043] (i) a substrate layer having coated thereon

[0044] (ii) an adhesion layer comprising a polymer having a glasstransition temperature of less than 15° C., said adhesion layer havingcoated thereon and bonded thereto

[0045] (iii) a hydrophilic layer

[0046] According to a further aspect of the present invention a methodfor the preparation of a planographic printing element suitable toreceive and bond with a subsequently applied hydrophilic layercomprises:

[0047] applying to a substrate a coating of a polymer having a glasstransition temperature of less than 15° C. said polymer containingfunctional groups capable of reacting with corresponding groups in thehydrophilic layer.

[0048] Preferably the polymer contains at least 25% by weight of amonomer containing a functional group

[0049] The polymer may be applied to the substrate as a compositioncontaining the polymer in admixture with gelatin, preferably in relativeamounts of from 95:5 to 5:95 preferably from 95:5 to 40:60 by weight.

[0050] In the case of a polyester or similar support, the adhesion ofthe adhesion layer thereto may be improved by the provision of a layerthat provides a key for the adhesion layer, or alternatively, by asurface treatment of the polyester with a corona or glow-discharge asdescribed in U.S. Pat. No. 4,689,359.

[0051] The above described method produces a printing element to which ahydrophilic layer will be applied to give a printing element that can beused in planographic printing. Therefore, after the application of theadhesion layer a subsequent step comprises applying a hydrophilicmaterial to the adhesion layer as a coating to form the hydrophiliclayer and provide a printing element that can be used in planographicprinting.

[0052] The invention is illustrated by reference to the followingExamples.

[0053] All the polymers used in the Examples had a glass transitiontemperature of less than 15° C.

EXAMPLE 1

[0054] Polymers A and B, shown below, were coated with a suitablecoating aid, in this case saponin (which is a surfactant) atapproximately 8.5 mg m⁻² of saponin.

[0055] Some coatings were composed polymer and saponin and othercoatings also contained gelatin.

[0056] The coatings were applied onto a polyester support with apre-applied hard undercoat layer (the purpose of which was to provide akey for the adhesion layer) to give a series of adhesion layers withvarying component laydowns.

[0057] Polymer A is poly(butyl acrylate-co-2-aminoethyl methacrylatehydrochloride-co-2-hydroxyethylmethacrylate), (50:5:45).

[0058] Polymer B is poly(butyl acrylate-co-2-aminoethyl methacrylatehydrochloride-co-2-methoxyethylmethacrylate), (50:5:45).

[0059] The resulting layers were then overcoated with a hydrophiliclayer comprising of a mixture of alumina and titania particles in asodium silicate binder, in a manner described fully in WO 97/19819, togive a total dry laydown of approximately 10 g m⁻².

[0060] The final coating structure is shown in FIG. 1 below.

[0061]FIG. 1 shows an optional hard undercoat layer (2) on the polyestersupport (1) which has been applied before the adhesion layer (3) toprovide a key therefor. The hydrophilic layer (4) is coated over theadhesion layer (3).

[0062] An alternative would be to apply the adhesion layer directly ontothe bare polyester support after the latter has been treated by coronaor glow-discharge as described for example in U.S. Pat. No 4,689,359.

[0063] These planographic printing elements were then evaluated foradhesion. The tests were performed by scoring the coatings with a razorblade in a grid pattern (five one inch lines, 0.2 inches apart andanother five lines at a 45 degree angle to the first set). A piece of610 scotch tape (3M company) was applied to the scored area and the taperapidly peeled off in an effort to remove the hydrophilic layer. Thecoatings were ranked using a scale of 1 to 6 where 6=Good (no removal ofthe coating) and 1=Poor (complete removal of the coating).

[0064] The results obtained from these tests, average values fromseveral coatings, are given in FIGS. 2 and 3.

[0065] It can be seen in FIG. 2 that as the laydown of Polymer A wasincreased the adhesion of the hydrophilic layer increased, producing aneffect superior to that obtained with gelatin alone. In addition, it wasalso possible to coat useful mixtures of Polymer A and gelatin. HoweverFIG. 3 shows that Polymer B (which contains no functional groups capableof bonding with the hydrophilic layer) had no useful effect and alsothat varying the laydown of polymer B had no discernible effect, even incombination with gelatin.

[0066] Polymer B is included for comparative purposes and does not formpart of the present invention.

EXAMPLE 2

[0067] Polymers C and D shown below were coated with a suitable coatingaid, in this case saponin at approximately 8.5 mg m⁻², and sometimeswith gelatin, onto a polyester support with a pre-applied undercoatlayer (*) to give a series of adhesion layers with varying componentlaydowns.

[0068] (* It would have been equally possible, but less experimentallyconvenient, to apply the adhesion layer directly to bare polyestersupport assisted by corona or glow-discharge treatments as demonstratedin the prior art noted above.)

[0069] Polymer C is poly(butyl acrylate-co-2-aminoethyl methacrylatehydrochloride-co-3-chloro-2-hydroxypropyl methacrylate), (50:5:45).Polymer D is poly(glycidyl methacrylate-co-butyl acrylate), (75:25).

[0070] The resulting layers were then overcoated with a hydrophiliclayer comprised of a mixture of alumina and titania particles in asodium silicate binder, in a manner described fully in WO 97/19819, togive a total dry laydown of approximately 10 g m⁻². The final coatingstructure is given in FIG. 1 above.

[0071] These planographic elements were evaluated for adhesion. Thetests were performed by scoring the coatings with a razor blade in agrid pattern (five one inch lines, 0.2 inches apart and another fivelines at a 45 degree angle to the first set). A piece of 610 scotch tape(3M company) was applied to the scored area and the tape rapidly peeledoff in an effort to remove the hydrophilic layer. The coatings wereranked using a scale of 1 to 6 where 6=Good (no removal of the coating)and 1=Poor (complete removal of the coating).

[0072] The results obtained from these tests, average values fromseveral coatings, are given in FIGS. 4 and 5 below.

[0073] It can be seen in FIG. 4 that as the laydown of Polymer Cincreased the adhesion of the hydrophilic layer, although the effect wasinferior to that obtained with gelatin alone. In addition, it was alsopossible to coat useful mixtures of Polymer C and gelatin. In the sameway, it can be seen in FIG. 5 that as the laydown of Polymer D wasincreased the adhesion of the hydrophilic layer increased, again, aneffect inferior to that obtained with gelatin alone.

[0074] As with Polymer C, it was also possible to coat useful mixturesof Polymer D and gelatin.

[0075] The invention has been described in detail with particularreference to certain preferred embodiments thereof, but it will beunderstood that variations and modifications can be effected within thespirit and scope of the invention.

What is claimed is:
 1. A planographic printing element suitable toreceive and bond with a subsequently applied hydrophilic layer saidelement comprising: (i) a substrate layer having coated thereon (ii) anadhesion layer, said adhesion layer comprising a polymer having a glasstransition temperature of less than 15° C. and containing functionalgroups capable of bonding with a hydrophilic layer when the latter isapplied as a coating.
 2. A planographic printing element as claimed inclaim 1 wherein the functional groups in the polymer are selected fromhydroxyl, epoxy and groups capable of being displaced by a nucleophilicgroup on the hydrophilic layer.
 3. A planographic printing element asclaimed in claim 2 wherein the polymer contains at least 25% by weightof a monomer containing a functional group.
 4. A planographic printingelement as claimed in claim 1 wherein the polymer is a copolymer of amonomer (i) containing the functional groups and a monomer (ii) such asan alkyl acrylate in relative amounts such that the glass transitiontemperature of the copolymer is less than 15° C.
 5. A planographicprinting element as claimed in claim 4 wherein the amount of monomer(ii) is from 15 to 75% by weight based on the combined weight of the twomonomers.
 6. A planographic printing element as claimed in claim 4wherein the polymer is a terpolymer containing a monomer (iii) toprovide the capability of crosslinking with gelatin by means ofconventional gelatin hardeners.
 7. A planographic printing element asclaimed in claim 6 wherein the amount of monomer (iii) is from 0.5 to10% by weight by weight of the combined weights of monomers (i), (ii)and (iii).
 8. A planographic printing element as claimed in claim 1wherein the adhesion layer comprises the polymer and gelatin in relativeamounts from 95:5 to 5:95 by weight.
 9. A planographic printing elementas claimed in claim 1 wherein the laydown of polymer or polymer andgelatin composition is from 50 mg/square metre to 4 g/square metre. 10.A planographic printing element comprising: (i) a substrate layer havingcoated thereon (ii) an adhesion layer, said adhesion layer comprising apolymer having a glass transition temperature of less than 15° C., saidadhesion layer having coated thereon and bonded thereto (iii) ahydrophilic layer.
 11. A planographic printing element as claimed inclaim 10 wherein the hydrophilic layer comprises metal oxide particlesand a silicate binder.
 12. A planographic printing element as claimed inclaim 11 wherein the metal particles comprise particles of titaniaand/or alumina.
 13. A method for the preparation of a planographicprinting element suitable to receive a hydrophilic layer subsequentlyapplied thereto which method comprises applying to a substrate a coatingof a polymer to form an adhesion layer said polymer having a glasstransition temperature of less than 15° C. and containing functionalgroups capable of reacting with corresponding groups in a subsequentlyapplied hydrophilic layer.
 14. A method as claimed in claim 13 whichfurther comprises applying a coating of a hydrophilic material to theadhesion layer to form a hydrophilic layer.
 15. A method as claimed inclaim 14 wherein the hydrophilic layer comprises metal oxide particlesand a silicate binder.